In deep water sport trolling at depths of about 100 to 300 feet for example, a fish-line sinker and bait cannot be used by themselves because they will not sink more than about 50 feet, because of the line floating and planing and because a heavy enough sinker cannot be used since it would be too much incumbrance upon hooking a fish. Thus a down-rigger is used to sink the fish-line and bait to the desired depth and a release device is used to allow the fish-line and bait to separate from the down-rigger when a fish is hooked on the bait, so that the fisherman has only the line, bait, and fish on his rod. A hoist, such as a hand-reel or a power-reel, has a beam extending over the side of the boat and a cable leads from the hoist to the end of the beam over a pulley and then downwardly to the weight which is usually one or more eight pound balls of lead. The release device is attached near the weight. The fish-line is attached to the weight or cable by a release device and the cable and fish-line are payed out at the same time with the weight to sink both to the desired depth. A length of fish-line or a leader trails from the release device to the bait.
However, with the prior art devices, the release device is such that it releases with about the same comparatively light force of pull from either the bait or the rod. Thus the fish-line cannot be tightened between the down-rigger and the rod and as a result the fish-line bows out rearwardly between the rod and the down-rigger providing too much slack in the line when a fish takes the bait. This slack prevents the angler from setting the hook in the fish without delay, gives the fish time delay to throw the hook, and delays the indication to the rod that the bait has been taken by a fish.
The round lead balls of the prior art used as down-rigger weights tend to come together aft of the boat and tangle the cables, lines, and baits. Also the prior art release devices on the pull of the rod let the fish-line detach without a fish on the bait and when this happens, the whole apparatus must be raised, reconnected, and again lowered.